Multi-electrode plasma processing apparatus

ABSTRACT

A multi-electrode plasma processing system (10) provides flexible plasma processing capabilities for semiconductor device fabrication. The plasma processing equipment (10) includes a gas showerhead assembly (52) a radio-frequency chuck (24), and screen electrode (66). The screen electrode (66) includes base (68) for positioning within process chamber (10) and is made of an insulating material such as a ceramic or teflon. A perforated screen (70) is integral to base (68) and generates a plasma from a plasma-producing gas via a radio-frequency power source (104). The screen (70) has numerous passageways (78) to allow interaction of plasma and the process chamber walls. The screen (70) surrounds showerhead assembly (52) and semiconductor wafer (22) and can influence the entire semiconductor wafer plasma processing environment (62) including the plasma density and uniformity. The circuitry (74) electrically connect screen (70) to a power source (100) or (104) to cause screen (70) electrode to affect process plasma density and distribution. Any of the plasma electrodes showerhead assembly (52), chuck (24), or screen electrode (66) may be connected to a low-frequency power source (108), a high-frequency power source (100 or 132), electrical ground (110), or may remain electrically floating (94).

The U.S. Government has a paid-up license in this invention and theright, in limited circumstances, to require the patent owner to licenseothers on reasonable terms as provided for by the terms of a contractwith the United States Air Force under the program name MMST.

This is a continuation of application Ser. No. 07/903,637, filed Jun.24, 1992 now U.S. Pat. No. 5,286,297.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to semiconductor waferfabrication processes, and more particularly relates to amulti-electrode, multi-zone plasma processing apparatus forsemiconductor wafer plasma processing for a variety of plasma-enhanceddevice processing applications.

BACKGROUND OF THE INVENTION

Manufacturers of electronic components use a variety of fabricationtechniques to produce semiconductor devices. One technique that has manyapplications (e.g., deposition, etching, cleaning, and annealing) isknown as "plasma-assisted" or "plasma-enhanced" processing.Plasma-enhanced processing is a dry processing technique in which asubstantially ionized gas, usually produced by high-frequency electricaldischarge, generates active metastable neutral and ionic species thatchemically react to deposit thin material layers on or to etch materialsfrom semiconductor substrates in a fabrication reactor.

Various applications for plasma-enhanced processing in semiconductormanufacturing include high-rate reactive-ion etching (RIE) of thin filmsof polysilicon, metals, oxides, and polycides; dry development ofexposed and silylated photoresist layers; plasma-enhanced chemical-vapordeposition (PECVD) of dielectrics, aluminum, copper, and othermaterials; planarized inter-level dielectric formation, includingprocedures such as biased sputtering; and low-temperature epitaxialsemiconductor growth processes.

Plasma-enhanced processes may use remotely-generated orlocally-generated plasmas. Remotely-generated plasma is a plasma that aplasma-generating device produces external to a fabrication reactor. Theplasma is guided into the main process chamber and there interacts withthe semiconductor wafer for various desired fabrication processes.Locally-generated plasma is a plasma that a plasma-generating chargedelectrode forms within the process chamber and around the semiconductorwafer from suitable process gases. Conventional plasma processingreactors for etch and deposition applications usually employ 13.56 MHzplasmas, 2.5 GHz remote plasmas, or a combination of these plasmas. Inconventional systems, a plasma-generating radio-frequency power sourceconnects electrically to a conductive wafer holding device known as awafer susceptor or chuck. The radio-frequency power causes the chuck andwafer to produce a radio-frequency plasma discharge proximate the wafersurface. The plasma medium interacts with the semiconductor wafersurface and drives a desired fabrication process such as etch ordeposition.

Opposite and parallel to the wafer and chuck in these systems is ashowerhead assembly for injecting the plasma-generating gas or gasmixtures into the process chamber. This is known as a parallel-plateconfiguration due the parallel surfaces of the chuck and showerhead.Typically, the showerhead connects to an electrical ground. In somedesigns, however, the showerhead assembly may connect to theplasma-generating radio-frequency power source, while the chuck andsemiconductor wafer connect to an electrical ground. Still otherconfigurations may use a combination of locally-generated plasma andremotely-generated plasma. In all of these known configurations, variouslimitations exist which contains the plasma process application domain.

Limitations associated with using only two parallel plates includeinefficient in-situ chamber cleaning and less than desirable processcontrol flexibility. In particular, the conventional parallel-plateconfiguration does not provide adequate control or adjustment overdeposited plasma process uniformity. Moreover, there is no independentcontrol over deposited film stress, deposition rate, and depositionuniformity. For example, a change in a process parameter to reduce filmstress may adversely affect deposition rate, and vice versa. Further, noindependent control over etch rate, selectivity, or anisotropy inplasma-enhanced etch and RIE processes occurs in these types of systems.

Consequently, there is a need for a semiconductor wafer fabricationprocess that overcomes the limitations of known systems to permitefficient in-situ chamber cleaning while providing necessary controlover plasma-enhanced fabrication processes.

There is a need for a method and apparatus for plasma-enhancedsemiconductor device fabrication that offers improved control over knownmethods and apparatuses. In particular, there is a need for aplasma-enhanced device fabrication method and system that improves thecontrol and adjustment of semiconductor wafer plasma processinguniformity.

There is a need for a semiconductor wafer fabrication method andapparatus that offers flexible control over film stress, depositionrate, and deposition uniformity in plasma-enhanced depositionapplications.

Furthermore, there is a need for a method and system that permitsflexible control over semiconductor wafer etch rate, selectivity, andanisotropy in plasma-enhanced RIE processes.

SUMMARY OF THE INVENTION

The present invention, accordingly, provides a plasma processing systemconfiguration for enhanced semiconductor wafer processing that overcomesor reduces disadvantages or limitations associated with prior plasmaprocessing methods and apparatus.

One aspect of the invention is a plasma processing system configurationfor enhanced semiconductor wafer processing in a fabrication reactorprocess chamber that includes a base that may be positioned within theprocess chamber and which is made of an electrically insulating materialsuch as a ceramic or teflon. A screen mounts integrally to the base andgenerally is made of an electrically conducting material that mayconduct a radio-frequency power for generating plasma from aplasma-producing gas or gas mixture. A plurality of passageways or holeson the screen permit interaction of the plasma environment with chamberwalls within the process chamber. The screen surrounds the semiconductorwafer, a showerhead that flows plasma-producing gases into the processchamber, and a radio-frequency chuck that holds the semiconductor wafer.By surrounding the wafer, the showerhead, and the radio-frequency chuck,the screen electrode of the present invention creates an environment formulti-electrode plasma processing proximate the semiconductor wafer. Theinvention further includes circuitry for electrically connecting thescreen electrode and other electrodes to various radio-frequency sourcesto produce a desired plasma processing environment.

A technical advantage of the present invention is that it significantlyfacilitates both in-situ chamber cleaning and semiconductor waferprocessing within the fabrication reactor process chamber. For example,the present invention permits flexible in-situ chamber cleaningintermittent with semiconductor wafer processing. Processes that thepresent invention permits include mixed remote-plasma andradio-frequency plasma processing, mixed radio-frequency magnetron andradio-frequency plasma processing, and mixed/multi-frequencymulti-electrode plasma processing.

Another significant technical advantage of the present invention is thatit enhances the capabilities for real time control of plasma processingparameters. These parameters include plasma process uniformity control,film stress control such as that occurring in plasma-enhancedchemical-vapor deposition, and sidewall angle or anisotropy controlduring plasma etch processing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its modes of use and advantages are best understood byreference to the following description of illustrative embodiments whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 provides a simplified schematic diagram of a representativesemiconductor wafer processing reactor plasma process chamber toillustrate the concepts of the preferred embodiment;

FIG. 2 shows a detailed schematic of a fabrication reactor processchamber that includes the preferred embodiment of the present inventionwithin a single-wafer advanced vacuum processor;

FIG. 3 provides an isometric view of the plasma processing screenelectrode of the preferred multi-electrode embodiment;

FIG. 4 illustrates possible multi-electrode/multi-frequencyradio-frequency connections usable with the preferred embodiment;

FIGS. 5 and 6, respectively, show side and top views of a firstpermanent magnet module usable to enhance operation of the preferredembodiment via magnetron plasma enhancement;

FIGS. 7 and 8, respectively, show side and top views of a secondpermanent magnet module usable with the preferred embodiment formagnetron plasma enhancement;

FIG. 9 shows a partitioned showerhead assembly for multi-electrodeand/or multi-frequency plasma processing with the preferred embodimentof the present invention;

FIG. 10 illustrates plasma time-division multiplexing for intermittentoxide PECVD and in-situ cleaning processes that the preferred embodimentmay employ;

FIG. 11 shows a representative time-division multiplexing (TDM)operation for interspersed PECVD silicon dioxide deposition and in-situplasma cleaning using the preferred embodiment;

FIGS. 12 and 13 show thickness uniformity profiles for PECVD oxidedeposition;

FIGS. 14 and 15 show uniformity profiles for PECVD oxide depositionusing the preferred embodiment and a two-zone plasma; and

FIG. 16 shows test results associated with aluminum-gate MOS capacitorswith oxide dielectrics made with the method and apparatus of thepreferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention is best understood byreferring to the Figures wherein like numerals are used for like andcorresponding parts of the various drawings.

The invention permits single-wafer plasma-assisted device fabrication,however, multi-wafer fabrication may also be accomplished using themulti-electrode configuration of the preferred embodiment. Processessuch as chemical-vapor deposition (CVD) and etch tend to leaveby-products or deposits on various parts and inner surfaces of theprocess chamber. One problem that chamber deposits from an earlierprocess may cause is adverse effects on process uniformity,repeatability, and particle contamination. In conventional plasmaprocessing, it is not possible to provide in-situ chamber cleaning witha high degree of cleaning process parameter control flexibility.Moreover, the conventional plasma processing methods do not provideflexible real time capabilities for plasma uniformity control and plasmaparameter adjustments provide hardware and process capabilities in orderto improve plasma processor capability and performance. To achieve theseresults, effective in-situ chamber cleaning during or after a depositionor etch process is particularly attractive. The preferred embodimentaccommodates these types of effective in-situ cleaning processes as wellas improved plasma processing capabilities.

In conventional single-wafer plasma processing chambers, a 13.56 MHzsource generates plasma discharge between two parallel plates. One platetypically is a radio-frequency chuck that holds the semiconductor wafer.The other is a metallic showerhead assembly that delivers theplasma-producing gases into the process chamber. Some designs power thechuck that hold the semiconductor wafer and connect the showerheadassembly to an electrical ground. Other designs power the showerheadassembly and ground the chuck. Limitations with this design include aninability to perform effective in-situ chamber cleaning, as well asgeneral inefficiency and lack of plasma process uniformity control.

The principal problem that causes lack of plasma process uniformitycontrol is the interdependence between various parameters during theplasma processing and lack of flexible process control parameters. Forexample, in conventional systems, essentially the only way to adjustplasma process uniformity is to vary process parameters that may impactthe plasma such as RF power, gas flow, or pressure. Changing theseparameters, however, may adversely affect other process parameters suchas deposition or etch rate and plasma-induced damage. The presentinvention permits flexible adjustment of plasma process uniformitywithout adversely affecting other important plasma process parameters.As a result, the effective in-situ chamber cleaning and flexible controlof the present invention provide increased process repeatability anduniformity as well as enhanced process cleanliness.

The following discussion describes how the preferred embodiment achievesthese and other objects of the present invention.

FIG. 1 shows a partially broken-away diagrammatic view of fabricationreactor plasma processing chamber 10 that may also include a magnetronmodule 12 above reactor chamber lid 14. Reactor chamber lid 14 hasseveral connector penetrations such as for thermocouple connections 16and 20 to permit wafer temperature sensing. For example, thermocoupleconnection 16 permits sensing semiconductor wafer 22 temperature. Otherpenetrations through reactor lid 14 to chuck 24 include chuck electrodeline 26 (described below as electrode line E₃) and coolant inlet 28 andoutlet 30. U.S. patent application Ser. No. 07/565,765 filed on Aug. 10,1990, by Mehrdad M. Moslehi and assigned to Texas InstrumentsIncorporated more particularly describes chuck 24 and is incorporated byreference herein.

Process chamber lid 14 joins reactor outer wall 32 at seal regions 34.Also, lid 14 contains support 36 that rests upon plasma chamber collar38 at contact seal 40. Support 36 also includes ledge 42 that supportsenclosure module 44 to hold chuck 24. Chuck 24 contacts semiconductorwafer 22 on bottom surface 46. Low thermal mass pins 48 and 50 supportsemiconductor wafer 22, causing it to maintain contact with chuck 24.Low thermal mass pins 48 and 50 are supported via showerhead assembly 52that includes showerhead injector 54.

Showerhead injector 54 permits the flow of plasma-producing gasesthrough gas channel 60 into showerhead injector 54 and throughperforated plate 56. Additionally, remotely-generated plasma may comefrom a plasma generating module (not shown) into the processingenvironment 62 for additional process activation.

Surrounding showerhead assembly 52 is perforated cylindrical electrodeor screen 66 of the preferred embodiment. Perforated cylindricalelectrode or screen 66 includes insulating base portion 68 andconductive screen portion 70. Additionally, multi-pole permanent magnetmodule 72 may be used to surround chamber collar 38 to induce magnetronenhancement within processing environment 62.

The hardware configuration of the plasma processing environment thatuses the preferred embodiment including cylindrical screen electrode 66includes three electrode lines that may be connected to radio-frequencyenergy source or electrical ground. These include electrode line E₁,designated as 74, to perforated cylindrical electrode or screen 66,electrode line E₂ to showerhead assembly 52, designated as 76, andelectrode line E₃, previously designated as 26, connecting to chuck 24.

FIG. 2 shows a detailed diagrammatic cut-away side view of the preferredembodiment to show an actual design within a single-wafer fabricationreactor plasma process chamber such as the Texas Instrument AutomatedVacuum Processor (AVP). Components with associated reference numerals inFIG. 2 operate and interconnect as described with reference to FIG. 1.

FIG. 3 more particularly illustrates perforated cylindrical or screenelectrode 66 of the preferred embodiment. Cylindrical electrode orscreen 66 includes base 68 made of an electrically insulating materialsuch as teflon or a ceramic material and upper portion or screen 70 madeof an electrically conducting material such as surface-anodizedaluminum. Within screen 70 are multiple holes or passageways such aspassageway 78 to permit plasma to communicate with the process chamberwalls for effective in-situ cleaning.

For the preferred embodiment, cylindrical electrode 66 must besufficiently large to surround showerhead 52 and sufficiently small tofit within the diameter of plasma process chamber collar 38. Insulating(teflon) base 68 must be sufficiently strong to support screen electrode70 and should be of an insulating material to electrically isolatescreen electrode 70 from the remainder of electrode conductivecomponents within plasma process chamber 10. Screen electrode 70 is aperforated cylinder sufficiently tall to cover the entire height ofplasma process environment 62 between showerhead assembly 52 and plasmachuck 24. Passing to and through insulating base 68 is electrode lead E₁74 which connects the screen electrode 70 to a radio-frequency powersource or an electrical ground. Depending on its connection modes screenelectrode 70 contributes to various modes of plasma generations forwafer processing and in-situ chamber cleaning.

FIG. 4 shows the multi-electrode/multi-frequency electrical connectionsfor electrode lines E₁ 74 to screen electrode 70, E₂ 76 to showerhead52, and E₃ 26 to chuck 24. Although other frequency sources may be usedwith the preferred embodiment, the electrical circuit diagram of FIG. 4is useful to illustrate essential concepts. Beginning with E₁ 74, switch82 includes rotatable connector 84 that may engage floating line contact86, high-frequency (e.g., a 13.56 MH_(z) RF source contact 88,low-frequency (e.g., 100 kH_(z) source) contact 90, and electricalground contact 92. Floating line contact 86 connects electrode line E₁74 to floating lead 94, so that screen 70 has no external electricalconnection and only minimally affects plasma within process chamber 10.Contact 88 connects electrode line E₁ 74 to high-frequency RF tuner 96.High-frequency RF tuner 96 receives control input 98 and transmits a13.56 MHz power signal from power source 100. This connection will causecylindrical screen electrode 70 to generate a 13.56 MHz plasma. Contact90 connects E₁ 74 through line 102 to low-frequency RF tuner 104.Low-frequency RF tuner 104 receives control input 106 and 100 kHz powerinput 108. By connecting electrode line E₁ 74 to low-frequency RF tuner104, cylindrical screen electrode 70 produces a 100 kHz plasma withinprocess chamber 10. Contact 92 connects electrode line E₁ 74 toelectrical ground 110 to cause grounding of plasma energy in theproximity of cylindrical electrode 66.

Switch 112 for electrode line E₂ 76 leading to showerhead assembly 52and switch 114 for electrode line E₃ 26 connecting to chuck 24 haveconnections similar to those of switch 82. In particular, rotatablecontact 116 of switch 112 connects electrode line E₂ 76 to electricalground 110 via contact 118, to low-frequency tuner 104 via contact 120,to high-frequency tuner 122 through contact 124, and to a floating lead126 via contact 128. High-frequency tuner 122 operates essentially thesame as high-frequency tuner 96, and includes control input 130 and13.56 MHz power input 132. Furthermore, switch 114 includes selectablecontact 134 for connecting to contact 136 for low-frequency RF energyfrom low-frequency RF tuner 104, contact 138 for input fromhigh-frequency RF tuner 122, connection to ground 140 via contact 142,and connection to floating line 144 via contact 146.

The multi-electrode, dual-frequency/radio-frequency connections of FIG.4 permit substantial flexibility and a capability for multi-zone plasmaprocessing. With the two high-frequency RF sources 106 and 132, togetherwith 100 kHz low-frequency RF source 108, numerous combinations ofplasma processing and in-situ cleaning may occur. Any one of the threeelectrodes E₁, E₂ or E₃ may be selectively connected to a floating lead,a high-frequency RF source, a low-frequency RF source, or to ground. Thefollowing discussions describe various connections for processes thatthe multi-electrode configuration of the preferred embodiment mayperform.

Fabrication Process Method 1

Connect electrode line E₁ 74 through select switch 84 to contact 86 forconnection to floating line 94. Connect electrode line E₂ 76 throughswitch 116 to ground 110 at contact 118, and electrode line E₃ 26through switch 134 to high-frequency RF tuner 122 via contact 138. Thisis a conventional mode of plasma-enhanced chemical-vapor deposition(PECVD) in which floating electrode line E₁ causes cylindrical screenelectrode E₁ to have minimal effect within process chamber 10.

Fabrication Process Method 2.

Connect electrode line E₁ to high-frequency RF tuner 96 by rotatingswitch 84 to contact 88, electrode line E₂ to ground by rotating switch116 to contact 118, and electrode line E₃ to high-frequency RF tuner 122by rotating switch 134 to contact 138. This connection permits dual-zoneplasma processing within process chamber 10. The radio- frequency powersof cylindrical screen electrode 66 from electrode line E₁ and chuck 24from electrode line E₃ may adjusted for optimal plasma processuniformity and/or minimal film stress. Note that this process may beperformed with more than two plasma zones such as in the alternativeembodiment of gas showerhead 184 in FIG. 9.

Fabrication Process Method 3

Connect electrode line E₁ to low-frequency RF tuner 104, line E₂ toground, and electrode line E₃ to high-frequency RF tuner 122. Thiscauses cylindrical screen electrode 66 to absorb a 100 kHz power thatproduces a low-frequency plasma, and radio-frequency chuck 24 to absorba 13.56 MHz power signal that enhances PECVD processing by controllinguniformity and/or stress. Thus, using this method, cylindrical screenelectrode 66 may generate a dense 100 kHz plasma that diffuses withinthe entire process chamber 10. The RF frequency of chuck 24 controls theion energy impinging on the wafer. This makes it possible to control thelayer stress through adjusting the ion energy. The power thatcylindrical screen electrode 66 receives may independently control thedeposition or etch rate, while the power that chuck 24 receives permitschuck 24 to control the layer stress and/or process uniformity.

Fabrication Process Method 4

Connect electrode line E₁ 74 to ground, electrode line E₂ 76 tohigh-frequency RF tuner 122, and electrode line E₃ 26 to ground. Thisyields a plasma process environment that permits deposition or etch withreduced ion energies on the wafer. Essentially, electrode E₂ provides a13.56 MHz power signal to showerhead assembly 52, while cylindricalscreen electrode 66 and chuck 24 are grounded. As a result, the ionenergy is reduced, thereby causing a softer impact of the ions on thewafer 22 surface.

Fabrication Process Method 5.

Connect electrode line E₁ 74 to high-frequency RF tuner 96, electrodeline E₂ 76 to ground, and electrode line E₃ 26 to low-frequency RF tuner104. In this PECVD process, cylindrical screen electrode 66 generatesprocess plasma, while chuck 24 controls ion energy and induced layerstress. This method is similar to process method 3, above, except thatwith process method 3, cylindrical screen electrode 66 absorbs a 100 kHzsignal plasma, while RF chuck 24 absorbs a 13.56 MHz signal to enhancethe PECVD processing and to control stress. This process method 5essentially reverses the connections that appear in process method 3. Asa result, RF chuck 24 produces a lower frequency output that mayincrease ion bombardment on wafer 22 surface. There are certain plasmaprocesses in which enhanced ion bombardment may be more desirable. Insuch instances, process method 5 is preferable to process method 3.

Fabrication Process Method 6

Connect electrode line E₁ to high-frequency RF tuner 96, electrode lineE₂ 76 to ground, and leave electrode line E₃ 26 floating. This causescylindrical electrode 66 to generate RF magnetron plasma. In thisprocess, a remote microwave plasma may be direct plasma to semiconductorwafer 22 with negligible ion energies.

Fabrication Process Method 7

Connect electrode line E₁ 74 to ground, electrode line E₂ 76 tolow-frequency RF tuner 104, and electrode line E₃ 26 to high-frequencyRF tuner 122. This method permits PECVD processing with continuous ionbombardment effects on showerhead assembly 52 and cylindrical electrode66. This process assists in preventing process chamber deposits, becauseit produces minimal ion bombardment on showerhead assembly 52 andelectrode 66.

Fabrication Process Method 8

Connect electrode line E₁ 74 to ground, electrode line E₂ 76 to floatingline 126, and electrode line E₃ to high-frequency RF tuner 122. Thismethod permits a PECVD process that has modified plasma processuniformity and ion energies.

Fabrication Process Methods 1 through 8, above, illustrate that thepreferred embodiment provides significant flexibility to yield optimalplasma process uniformity, rate control, and layer stress control duringplasma-enhanced semiconductor device fabrication. Additionally, becausethe connections from electrode lines E₁ 74, E₂ 76, and E₃ 26 throughswitches 82, 112, and 114, respectively, to the various ground, floats,and power sources may be made in real time, additional process parametercontrol flexibility results.

Not only does the preferred embodiment permit flexibility in etching andother wafer fabrication processes, but also the preferred embodimentprovides significantly enhanced in-situ chamber cleaning flexibilities.In particular, the preferred embodiment permits effective in-situchamber cleaning in real time associated with wafer etch and depositionprocesses. For example, the in-situ cleaning that preferred embodimentprovides may be performed after each PECVD process, such as fordeposition of silicon dioxide, silicon nitride, amorphous silicon, etc.to remove any residual deposits from process chamber 10 inner surfaces.Showerhead assembly 52 and chamber collar 38 may hold residual depositsor contaminants for which removal is necessary. For removing theseresidual deposits, chamber cleaning chemistry may include a plasma suchas a combination of argon and CF₄, or argon and NF₃, or argon and SF₆.Various methods for in-situ cleaning with the preferred embodiment mayuse the following electrode connections.

Cleaning Process Method 1

Connect electrode line E₁ 74 to ground, electrode line E₂ 76 tolow-frequency RF tuner 104, and electrode line E₃ 26 to ground 20. Thisconfiguration causes plasma generation and impact of high energy etchions on the surface of showerhead assembly 52 to permit showerheadassembly 52 cleaning.

Cleaning Process Method 2

Connect electrode line E₁ 74 to low-frequency RF tuner 104, electrodeline E₂ 76 and electrode line E₃ 26 to ground. These connections yield aplasma environment for cleaning process chamber collar 38 within processchamber 10 via the screen electrode 66.

Cleaning Process Method 3

Connect electrode lines E₁ 74 and E₂ 76 to ground, and electrode line E₃24 to low-frequency RF tuner 104. These connections clean any residualdeposits from the RF chuck 24.

Cleaning Process Method 4

Connect electrode line E₁ 74 to ground, electrode line E₂ 76 tolow-frequency RF tuner 104, and electrode line E₃ to high-frequency RFtuner 122. This configuration intensifies the plasma energies forcleaning showerhead assembly 52.

FIGS. 5 and 6, respectively, show a side and top view of magnetronpermanent magnet assembly 72 that the preferred embodiment may use.Magnetron permanent magnet assembly 72 permanent magnet assembly has aheight 150 sufficiently tall to span the height of process environment62 within process chamber 10. Moreover, magnetron permanent magnetassembly 72 has an outer diameter 152 sufficiently small so thatassembly 72 fits within reactor casing wall 32 and an inner diameter 154sufficiently large so that, when combined with the width 156 of twomagnets such as magnets 158 and 159 that permanent magnet assembly 72fits easily around process chamber collar 38. Magnets such as magnets158 are positioned, in the embodiment of magnetron permanent magnetassembly 72, to be 30° apart radially with alternating north and southpoles contacting magnetron outer wall 160. That is, if magnet 158, forexample, has its north pole contacting wall 160 and its south polefacing the inner portion of magnetron 72, magnet 162 adjacent to magnet158, has its south pole contacting outer wall 160 and its north poledirected to the magnetron 72 center. In the embodiment of FIGS. 5 and 6,separating magnets 158 and 162 by 30° with alternating north and southpoles contacting outer wall 160 permits the placement of 12 such magnetsalong the inner diameter of outer wall 160.

FIGS. 7 and 8, respectively, show side and top views of an alternativemagnetron permanent magnet assembly 164 that may be used with thepreferred embodiment of the present invention. Referring to FIG. 7,magnets such as magnet 166 are positioned with a vertical orientation sothat the north (or south) pole 168 is at the top and south (or north)pole 170 is at the bottom of wall 169 and contacts base 172 ofalternative magnetron permanent magnet assembly 164. Note thatalternative magnetron assembly 164 has the same space limitations asmagnetron assembly 72 of FIGS. 5 and 6, above. Thus, outer diameter 174must be sufficiently small to fit within reactor casing wall 32 whileinner diameter 176 must be sufficiently large to fit around processchamber collar 38. As opposed to having alternating north and southpoles as in magnetron 72 of FIGS. 5 and 6, magnetron 164 has all magnetsmagnetized vertically with the same orientation. Also appearing at andabove north poles 168 of magnets such as magnet 166 is a soft iron ring178 that serves to limit the propagation of the magnetic field from themagnets 166.

A general distinction between magnetron assembly 72 of FIGS. 5 and 6 andmagnetron assembly 164 of FIGS. 7 and 8 is the flux distribution thatthe respective orientations produce. For example, magnetron assembly 72of FIGS. 5 and 6 form a multipolar magnetic field inside process chambercollar 38. Moreover, the arrows 182 of FIG. 7 show the top-to-bottommagnetic flux distribution that the vertically oriented magnets ofmagnetron assembly 164 produce. Although using magnetron permanentmagnet assemblies 72 or 164 enhances screen electrode plasma density forthe preferred embodiment, their use is optional for the essentialpurposes of the present invention.

FIG. 9 shows an alternative configuration of showerhead assembly 52 thatprovides multiple showerhead electrode zones for multi-zone plasmaprocessing. Referring to FIG. 9, alternative showerhead assembly 184includes concentric plasma electrode rings such as outer concentric ring186, middle concentric ring 188, and inner disk 190 that connect,respectively, to outer showerhead electrode line E₂ ' 192, middleelectrode line E₃ ' 194 and inner electrode line E⁴ ' 196. Separatingconcentric showerhead portions 186, 188 and 190 is an insulatingmaterial 198 and 200 that may be made of macor, teflon, ceramic or someother electrically insulating material. Note that this configurationprovides three showerhead electrode connections 186, 188, 190, plus thescreen electrode 66 and chuck 24. This is a total of five plasmaelectrodes for multi-zone plasma processing. The relativeradio-frequency power to the showerhead electrodes can be adjusted tooptimize plasma process uniformity.

FIG. 10 illustrates how a cleaning and PECVD process may betime-division multiplexed in real time using the preferred embodimentfor silicon dioxide deposition. For example, line 202 may indicate flowof diethylsilane (DES) gas beginning at t_(o) and zero level 204. Attime t₁, flow increases to finite flow level 206. Also, at time to, line208 represents the flow of NF₃ cleaning gas beginning at high level 210.At time t₁, NF₃, gas flow drops to low (zero) level at 212. For apredetermined time, the DES gas will flow until, at time t₂ DES gas flowdrops, again, to low or zero level at 204, and NF₃ cleaning gas returnsto its high level at 210. At this point, a chamber cleaning processoccurs until, at time t₃, flow of cleaning gas NF₃ goes to low or zerolevel at 212, while DES returns to high level at 206. This type of gasflow chopping may occur while electrode line E₃ to RF chuck 24 connectsto high-frequency RF tuner 122, electrode line E₂ 76 for showerhead 52connects to low-frequency RF tuner 104, and electrode line E₁ forcylindrical screen electrode 66 connects to ground 110.

The time lines of FIG. 11 employ the basic concepts of FIG. 10 to showan illustrative example of PECVD silicon dioxide deposition using acombination of TEOS or DES, oxygen, and argon with a cleaning gascombination of NF₃, oxygen, and argon in a time-division multiplexing orchopping mode. Referring to FIG. 11, line 214 represents the flow of DESor TEOS gas, line 216 represents the flow of argon gas, line 218represents the flow of oxygen and line 220 represents the flow of NF₃gas. Line 222 represents the total pressure within process chamber 10occurring as a result of the process gas flow. At the same time that gasflows change, lines 224, 226 and 228 profile the radio-frequency signalsto electrode line E₃, E₂, and E₁, respectively.

Beginning at time t_(o), DES gas goes from zero level 230 to high level232, argon gas goes from zero level 233 to high level 234, oxygen gasflow rises from zero level 235 to high level 236, and NF₃ gas levelremains at constant zero level 238. As a result of gas flow beginning inprocess chamber 10, pressure line 222 indicates a process chamberpressure rise to level 240. Referring to the electrode lines E₃, E₂, andE₁, at time to electrode line E₃ to RF chuck 24 receives a 13.56 MHzsignal indicated by level 242, electrode line E₂ to showerhead 52connects to ground, and electrode line E₁ receives a 13.56 MHz signalfrom high-frequency RF tuner 96 as level 246 indicates. During thisphase of this exemplary process, a deposition of silicon dioxide mayoccur on wafer surface 22 in the environment 62 of process chamber 10.

At t₁, process parameters change in the exemplary process. DES flowreturns to off level 230, electrode line E₃ connects to ground causingthe signal to drop to zero level 248, and electrode line E₁ connects toground as the drop to zero level 250 shows. As a result of the change ingas flow, pressure line 222 may show a momentary slight pressure dip 252followed by a rapid return to previous pressure level 240 (viaclosed-loop pressure controller).

At time t₂ cleaning within process chamber 10 begins by introducing NF₃gas. NF₃ gas flow goes from low or zero level 238 to high level 254.Electrode line E₁ to cylindrical screen electrode 66 receives a 100 kHzsignal from low-frequency RF tuner 104. The line 228 transition to level246 represents this change. At this point, pressure within processchamber 10 may show a minor increase or bump such as the increase tolevel 258 followed by rapid return to the steady-state level 240.

At time t₃, in-situ cleaning ceases as NF₃ gas flow, 100 kHz signal toelectrode E₁, and electrode E₁ power return to zero levels. At thispoint, pressure momentarily dips to level 252 and then returns to level240.

At time t₄, a second cycle of silicon dioxide deposition occurs. Forthis process, DES gas line 214 shifts from zero level 230 to high level232, electrode line E₃ connects to high-frequency RF tuner 122, andelectrode E₁ connects to high-frequency RF tuner 96. All other processparameters remain the same. This change in gas flow causes momentarypressure bump 258.

At time t₅, this second deposition ceases when DES gas flow ends, andthe 13.5 GHz signals terminate as electrode lines E₃ and E₁ connect toground. Pressure again dips to low level 252 to return to steady-statelevel 240.

At time t₆, a second cleaning process cycle begins with NF₃ gas flowgoing from level 238 to level 254 and electrode line E₂ connecting to a100 kHz signal from low-frequency RF tuner 104. This in-situ cleaningprocess ceases at time t₇ when NF₃ gas flow, returns to zero level 238and electrode line E₂ voltage returns to ground 110. With NF₃ gas flowceasing, pressure within process chamber 10 dips momentarily to level252.

At time t₈, yet a third deposition process cycle is used. This thirddeposition process begins as DES gas goes to level 232, electrode lineE₃ connects to high-frequency RF tuner 122 to receive 13.56 MHz signal,and electrode line E₁ connects to high-frequency RF tuner 96 to alsoreceive a 13.56 MHz signal. The change in gas flow causes a temporarybump in process chamber pressure to level 258. This third depositionprocess will continue until it, at time t₉, DES gas flow returns to zerolevel 230, electrode line E₃ returns to ground level 248, and electrodeline E₁ returns to ground level 250. This change also causes momentarypressure dip 252.

At time t₁₀, yet a third in-situ cleaning process within chamber 10occurs as NF₃ gas flow goes to level 254, and electrode line E₁ connectsto low-frequency RF tuner 104 to receive a 100 kHz signal. Momentarypressure bump 258 evidences this change in plasma gas flow. At time t₁₁,the cleaning process ceases as NF₃ gas returns to low level 238 andelectrode line E₁ returns to ground potential 250. Pressure dip 252, attime t₁₁, is a result of this change in NF₃ gas flow.

A fourth and final deposition process cycle occurs when, at time t₁₂,DES gas flow goes to level 232, electrode E₃ receives a 13.56 MHz signalfrom high-frequency RF tuner 122 and electrode E₁ receives a 13.56 MHzsignal from high-frequency RF tuner 96. This process cycle continuesuntil, at time t₁₃, it ceases. Also, at time t₁₃ the PECVD silicondioxide deposition and cleaning processes cease. DES gas flow returns tozero level 230, argon gas flow 216 drops to level 233, oxygen gas flow218 drops to level 235, NF₃ gas flow remains at level 238, pressuredrops to pre-process vacuum level 239, electrode E₃ (line 224) drops toground potential 248, electrode E₂ remains at ground level 244, andelectrode E₁ line potential drops to ground level 250. This completesthe process of FIG. 11. The above-mentioned process shows an example ofa time-division multiplexed PECVD process along with in-situ cleaningvia multi-electrode plasma processing.

FIGS. 12 through 15 show results obtainable using the preferredembodiment of the present invention on 150 mm wafers. In particular,FIGS. 12 and 13 show examples of PECVD DES oxide deposition uniformitymeasurements for processes occurring using two different sets of processparameters. FIG. 12 shows the results of flowing 500 standard cubiccentimeters per minute (SCCM) of argon, 100 SCCM of oxygen, and 25 SCCMof DES in a plasma process chamber at a pressure of 3 Torr. Cylindricalscreen electrode 66 connects via electrode line E₁ to ground, showerheadelectrode 76 receives via electrode line E₂ 10 watts of a 100 kHz signalfrom low-frequency RF tuner 104, and radio-frequency chuck 24 connectsvia electrode line E₂ to 50 watts of 13.56 MHz power such as that fromhigh-frequency RF tuner 122. The following table shows statisticalvariations appearing in the wafer results that FIG. 12 illustrates.

                  TABLE I                                                         ______________________________________                                        MEAN      7574. Å      WAFER    150.00 mm                                 THICKNESS                  DIA.     /5.91 in                                  STD DEV   220.08 Å                                                                           2.905%  TEST     140.00 mm                                 MINIMUM   6990.2 Å     DIA.     /5.91 in                                  MAXIMUM   7984.0 Å     CONTOUR  STANDARD                                                             DISPLAY                                                                       INTERVAL 58.000                                    ______________________________________                                    

Similarly, FIG. 13 shows measurements taken after a PECVD process with100 SCCM argon, 100 SCCM oxygen, and 25 SCCM DES gas flows performed ata pressure of 1 Torr. In the process of FIG. 13, cylindrical screenelectrode 66 is floating, RF chuck 24 receives 50 watts of a 13.56 MHzsignal from RF tuner 122, and showerhead electrode 76 connects toground. Table II shows the statistical results that process achieved.

                  TABLE II                                                        ______________________________________                                        MEAN      5847.2 Å     WAFER    150.00 mm                                 THICKNESS                  DIA.     /5.91 in                                  STD DEV   198.69 Å                                                                           3.398%  TEST     140.00 mm                                 MINIMUM   5.510.1 Å    DIA.     /5.51 in                                  MAXIMUM   6201.1 Å     CONTOUR  STANDARD                                  NUMBER OF 49/46            DISPLAY                                            SITES/GOOD                 INTERVAL 68.000                                    ______________________________________                                    

Table III shows exemplary results for deposition rate in angstroms perminute using the multi-zone, multi-electrode plasma processes of thepreferred embodiment at two different pressures. As shown, the higherpressure PECVD process results in a higher deposition rate.

                  TABLE III                                                       ______________________________________                                        PRESSURE (Torr)                                                                            1             3                                                  RATE (ang/min)                                                                             1300          1700                                               Ar (sccm)    100           500                                                TEOS (sccm)  25            100                                                O2 (SCCM)    100           100                                                RF@ chuck    50 W,13.56 MH.sub.z                                                                         50 W,13.56 MHz                                     RF@ showerhead                                                                             grounded      grounded                                           RF@ perforated                                                                             20 W,100 kH.sub.z                                                                           20/W, 100 kH.sub.z                                 screen                                                                        ______________________________________                                    

FIGS. 14 and 15 further show the PECVD oxide thickness uniformitycontrol achievable using the multi-zone plasma processing apparatus ofthe preferred embodiment. The process of FIG. 14 uses 500 SCCM of argon,100 SCCM of oxygen, and 25 SCCM of DES with a 3-Torr process pressure.Cylindrical screen electrode 66 connects to ground, showerhead assembly52 connects to ground, and RF chuck 24 receives 50 watts of 13.56 MHzsource. Table IV shows the statistical results of this process.

                  TABLE IV                                                        ______________________________________                                        MEAN     11321.0 Å     WAFER    150.00 mm                                 STD DEV  463.70 Å                                                                            4.096%  DIA.     /5.91 in                                  MINIMUM  9535.5 Å      TEST     140.00 mm                                 MAXIMUM  11933 Å       DIA.     /5.51 in                                                             CONTOUR  STANDARD                                                             DISPLAY                                                                       INTERVAL 160.00                                    ______________________________________                                    

Finally, FIG. 15 shows the results of a process that uses 500 SCCM ofargon, 100 SCCM of oxygen, and 25 SCCM of DES at a 3 Torr processpressure. Electrode line E₁ 74 connects to a 15 watt 100 kHzlow-frequency source such as RF tuner 104, electrode line E₂ 76 connectsto ground, and electrode line E₃ 26 receives 50 watts of 13.56 MHzsource such as that from RF tuner 122. Table V shows the statisticalresults of this process. As shown, this PECVD process with multizoneplasma generation provides improved oxide thickness uniformity comparedto the single-zone plasma deposition process of Table IV. Themulti-electrode plasma configuration allows adjustments of relative zoneplasma densities in order to optimize the overall process uniformity.Note that all the PECVD processes were performed at approximately 400°C.

                  TABLE V                                                         ______________________________________                                        MEAN     12075 Å       WAFER    150.00 mm                                 STD DEV  346.25 Å                                                                            2.868%  DIA.     /5.91 in                                  MINIMUM  10582 Å       TEST     140.00 mm                                 MAXIMUM  12734 Å       DIA.     /5.51 in                                                             CONTOUR  STANDARD                                                             DISPLAY                                                                       INTERVAL 160.00                                    ______________________________________                                    

FIG. 16 shows the device electrical results that the multi-electrode,multi-zone plasma processing method and apparatus of the preferredembodiment provide. In particular, FIG. 16 shows electrical breakdownmeasurements on aluminum-gate metal-oxide semiconductor (MOS) capacitorswith PECVD oxide gate dielectrics using the preferred embodiment.Referring to FIG. 16, along the vertical axis 300 appear percentagedielectric failures ranging from 0% to 100%. Along horizontal axis 302appear measurements of electrical breakdown fields for the capacitors inmeasures of megavolts per centimeter ranging from 0 MV/cm to 14 MV/cm.The process requirement specification for the capacitors in this exampleis that mean breakdown must occur above 4 MV/cm. As FIG. 16 illustrates,those capacitors formed at a process pressure of 1 Torr have a breakdownfield generally ranging between 6 and 10 MV/cm. The breakdown field forcapacitors formed in a 3 Torr process is between 4 and 7 MV/cm,approximately. Generally, all breakdowns occur above the 4 MV/cmrequirement. These results indicate the acceptable electrical quality ofthese PECVD oxide layers from the method and apparatus of the preferredembodiment.

Although the invention has been described with reference to theabove-specified embodiments, this description is not meant to beconstrued in a limiting sense. Various modifications of the disclosedembodiment, as well as alternative embodiments of the invention willbecome apparent to persons skilled in the art upon reference to theabove description. It is therefore, contemplated that the appendedclaims will cover such modification that fall within the true scope ofthe invention.

What is claimed is:
 1. A method for plasma-enhanced processing usingmulti-electrode plasma generation in a process chamber, comprising thesteps of:holding a semiconductor wafer against a chuck electrode;injecting a plasma-producing gas through a showerhead electrode to thesurface of a semiconductor wafer; and producing a plasma from saidplasma-producing gas wherein said plasma interacts with the walls of theprocess chamber through a peripheral chamber wall electrode having aconducting screen.
 2. The method of claim 1, further comprising the stepof:selectably connecting one of a plurality of voltage sources to saidchuck electrode; selectably connecting one of said plurality of voltagesources to said showerhead electrode; and selectably connecting one ofsaid plurality of voltage sources to said peripheral chamber wallelectrode.
 3. The method of claim 2, wherein said plurality of voltagesources comprises a high frequency rf source, a low frequency rf sourceand ground.
 4. The method of claim 3, wherein said plurality of voltagesources further comprises a floating source.
 5. The method of claim 1wherein said showerhead electrode comprises a first electrode ring, asecond electrode ring concentric about said first electrode ring and athird electrode ring concentric about said second electrode ring.
 6. Themethod of claim 5, further comprising the steps of:connecting a firstelectrical signal to said first electrode ring of said showerheadelectrode; connecting a second electrical signal to said secondelectrode ting of said showerhead electrode; and connecting a thirdelectrical signal to said third electrode ring of said showerheadelectrode.
 7. The method of claim 1, further comprising the step ofproducing a magnetic field in said process chamber.
 8. The method ofclaim 1, further comprising the step of time-division multiplexing saidstep of injecting said plasma-producing gas with a step of injecting acleaning gas to create a plasma for cleaning said walls of said chamber.9. The method of claim 1, wherein said plasma producing gas is a chambercleaning gas chemistry.
 10. The method of claim 1, further comprisingthe steps of:connecting a high frequency rf voltage source to said chuckelectrode; connecting a ground voltage to said peripheral chamber wallelectrode; and connecting said showerhead electrode to a low frequencyrf voltage source to create an electric field in said process chamber,wherein the step of flowing a plasma-producing gas comprises the stepsof: flowing a plasma producing gas through said electric field for afirst time period to create a first plasma; flowing a cleaning gasthrough said electric field for a second time period after said firsttime period to create a second plasma for cleaning said walls of saidprocess chamber; and repeating both said flowing steps a number oftimes.
 11. The method of claim 1, further comprising the stepsof:connecting said chuck electrode to a high frequency rf voltagesource, said showerhead electrode to a ground voltage, and saidperipheral chamber wall electrode to said high frequency rf voltagesource to create a first electric field prior to said step of injectingsaid plasma producing gas; switching said chuck electrode to said groundvoltage and said peripheral chamber wall electrode to a low frequencyvoltage source to create a second electric field after said step ofproducing a plasma; injecting a cleaning gas through said showerheadelectrode to said second electric field to create a plasma for cleaningsaid walls of said process chamber; switching said chuck electrode tosaid high frequency rf source and said peripheral chamber wall electrodeto said high frequency rf source to recreate said first electric fieldafter said step of injecting said cleaning gas; injecting saidplasma-producing gas through said showerhead electrode into said firstelectric field to create a plasma; switching said chuck electrode tosaid ground voltage, said showerhead electrode to a low frequencyvoltage source, and said peripheral chamber wall electrode to saidground voltage to create a third electric field; injecting said cleaninggas through said showerhead electrode to said second electric field tocreate a plasma for cleaning said walls of said process chamber; andrepeating the above steps a number of times.